During the last few days while I was trying UHF Packet on the international space station .I noticed several time a sudden dip in the signal strength and loss in connection with packet system. ISS elevation was reasonable and the signal strength on the VHF packet system was strong!
I’m thinking of 3 cases:
1- The patch antennas position!
(The patch antennas are fixed on the Meteorite Debris Panels (MDP) protecting the hull of Columbus. On the port cone of the module, where it attaches to the ISS )
2- Radio and power used!
3- Doppler Effect!
As long as the signal dip was sharp and suddenly
And the transceiver was drive by Doppler shift correction software
I think the position of patch antennas plays the major role for the sudden signal strength weakness.
More Information needed to confirm this notice.